For example, in order to drill a hole in concrete and stone or the like, it is generally conducted to attach an exclusive drill bit to a rotating hammer drill and simultaneously give a vibratory impact along the axial direction and a rotating torque to the drill bit. In order to satisfy the demand for high efficiency of the drilling work, the steel drill bit, to the end of which a good wear-resistant cutting edge tip made of sintered hard alloy was fixed by brazing, welding or the like, is employed for the drill bit. For example, Japanese patent laid-open application publication No. Hei 7-180463 discloses the following drill: The cutting edge tip has a rectangular section. Main cutters are formed along one diagonal of the end. Auxiliary cutters are formed along the other diagonal of the end. Two main cutters which are opposed to each other form a chisel edge at the top.
The cutting edge tip of the drill bit employs the following constitution to carry out the machining function. A hard metal made of metallic carbide, which has a relatively higher hardness and strength with wear resistance, is mainly employed for the material of the nose. A bonding metal such as cobalt or the like which has a relatively lower hardness with toughness, is mainly employed for the material of the bonding side which bonds the cutting edge tip to the main part of the drill bit. That is, the material of the nose side of the cutting edge tip is needed to have wear resistance, and the material of the bonding side of the cutting edge tip is needed to contain much material which is easily bonded to the other material and have a near coefficient of thermal expansion to that of the other material. Thus, the different properties are necessary for the nose side and the bonding side of the cutting edge tip to be bonded to the end of the drill bit.
Japanese Patent laid-open application publication No. Hei 8-100589 discloses the following drill bit: The drill bit consists of a bit head which forms a contact surface with rock surface or rocky mountain and a stem portion which is an attachment part to a device. The bit head consists of a head tip portion and a fitting portion which is integrally fusion-welded with the base of the head tip portion and fitted to the stem portion. The head tip portion is harder than the fitting portion and the hardness of the head tip portion made of sintered hard alloy is gardient so that the hardness of the end is higher than the base.
Japanese Patent laid-open application publication No. Hei 8-170482 discloses the following drill bit: The drill bit consists of a head tip portion which plays a leading role in the drilling work to rock surface or rocky mountain and a shank portion which is an attachment part to a device. The head tip portion is integrally fusion-welded with the shank portion. The hardness of the head tip portion made of sintered hard alloy is gardient so that the hardness of the end is higher than the base adjacent to the shank portion.
Japanese Patent laid-open application publication No. 2006-118033 discloses a method for producing a sintered body having a gradient chemical composition by pulse charging sintering.
Japanese Patent publication No. Hei 10-511740 based on an international application and Japanese Patent laid-open application publication No. Sho 61-231104 disclose the following metallic product: The metallic product consists of first portion and second portion. The first portion comprises wear-resistant coarse metallic particles and the second portion comprises wear-resistant fine metallic particles. The bonding metal content of the first portion is small and the bonding metal content of the second portion is large.